Overhead Cast Iron DWV pipe replacement in basement

I am working to finish out my basement in my house which was built in 1938 and I am looking to replace the cast iron DWV lines that are overhead in the basement with PVC to get them up into the joists to increase the ceiling height and because they are starting to look a bit worse for the wear. My plan is to leave the vertical stacks in the walls as they are in good shape and only replace the horizontal lines. My question is: If I don't touch the vertical stack in the walls and I'm only replacing the overhead horizontal lines in the basement and connecting to the vertical stacks with Fernco fittings are the vertical stacks gonna come crashing down on me if I cut the horizontal pipes loose?" Again, I'm not replacing any section of the vertical cast stack, only the horizontal pieces in the basement that connect to it. Thanks for any help you might be able to give!

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Overhead Cast Iron DWV pipe replacement in basement

The only way to be certain is to open up the wall above where the vertical section penetrates the floor above and see if there are is any kind of riser clamp type support in the wall (or it's 1930's equivalent). It may look something like this;

Having said that I cannot believe that there would be an inordinate amount of weight on the horizontal joints, as they would have leaked a few thousand times since the original install. Or the original cast hubs would have cracked, even if they're packed with lead & oakum. How is the cast iron joined? How is the horizontal cast supported?

Overhead Cast Iron DWV pipe replacement in basement

The original horizontal cast is supported with a few pieces of metal "pipe strap" but I can't imagine that is the only thing that is supporting those stacks running through the walls? As for the pipe joints, they are the lead and oakum joints. There isn't any evidence at all in any of the pipes of any sort of cracking at all. The main problem is that one of the pipes run over my electrical panels with a joint directly above one of the panels so if it ever decided to leak....well you know where that would get me. Any additional thoughts / help would be appreciated!!